The alteration of the DNA of a living cell is likely to affect either its capacity to survive or the content of its store of genetic information. Agents such as ionizing radiation, radiation sensitizers and repair inhibitors affect cell survival and mutation probabilities because of their effects, either direct or indirect, on the structure and function of nucleic acids. These agents are referred to collectively as biocatastrophic agents. To understand the function of these agents, it is proposed to study the three-dimensional atomic arrangement of these molecules by single crystal x-ray diffraction techniques. The detailed knowledge of the structure of these agents along with information regarding the nature of their interaction with nucleic acid components as obtained by various physicochemical methods in addition to x-ray crystallography is expected to add considerable depth to our understanding of these biocatastrophic processes.